The present invention relates to a fuel assembly for a boiling water nuclear reactor, which fuel assembly comprises a plurality of vertical fuel rods arranged between a bottom tie plate and a top tie plate in a surrounding casing part, the lower end of which is connected to a bottom part which is provided with an inlet opening for water for conducting water in through the bottom tie plate, through the space between the fuel rods in the vertical casing part, and out through the top tie plate.
Experience shows that, for example in connection with repair and service of a nuclear reactor, debris may enter, which debris then moves with the water which circulates through the reactor core. The debris may, for example, consist of metal chips (borings) formed in connection with repair of, for example, a steam separator, pieces of metal wire, or other foreign particles which have entered the system from outside. The debris may give rise to abrasion damage, which has serious consequences if the damage arises on parts which are particularly easily damaged, such as fuel rods.
To avoid damage of the above-mentioned kind in pressurized water reactors, it is known to provide the bottom tie plates which already exist below the fuel rod bundle with a large number of holes to enable each bottom tie plate, in addition to each normal function, to function as a debris catcher in the form of a strainer and prevent debris from reaching the fuel rod bundle with control rod guide tubes and spacers.